Methods for forming structures for MRAM applications

ABSTRACT

Embodiments of the disclosure provide methods and apparatus for fabricating magnetic tunnel junction (MTJ) structures on a substrate in for hybrid (or called integrated) spin-orbit-torque magnetic spin-transfer-torque magnetic random access memory (SOT-STT MRAM) applications. In one embodiment, the method includes one or more magnetic tunnel junction structures disposed on a substrate, the magnetic tunnel junction structure comprising a first ferromagnetic layer and a second ferromagnetic layer sandwiching a tunneling barrier layer, a spin orbit torque (SOT) layer disposed on the magnetic tunnel junction structure, and a back end structure disposed on the spin orbit torque (SOT) layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/195,313 filed Nov. 19, 2018, the contents of which are incorporatedherein by reference in its entirety.

FIELD

Embodiments of the disclosure relate to methods for fabricatingstructures used in magnetoresistive random access memory (MRAM)applications. More specifically, embodiments of the disclosure relate tomethods for fabricating magnetic tunnel junction structures for MRAMapplications.

BACKGROUND

Magnetoresistive random access memory (MRAM) is a type of memory devicecontaining an array of MRAM cells that store data using their resistancevalues instead of electronic charges. Generally, each MRAM cell includesa magnetic tunnel junction (MTJ) structure. The MTJ structure may haveadjustable resistance to represent a logic state “0” or “1.” The MTJstructure typically includes a stack of magnetic layers having aconfiguration in which two ferromagnetic layers are separated by a thinnon-magnetic dielectric, e.g., an insulating tunneling layer. A topelectrode and a bottom electrode are utilized to sandwich the MTJstructure so electric current may flow between the top and the bottomelectrode.

One ferromagnetic layer, e.g., a reference layer, is characterized by amagnetization with a fixed direction. The other ferromagnetic layer,e.g., a storage layer, is characterized by a magnetization with adirection that is varied upon writing of the device, such as by applyinga magnetic field. In some devices, an insulator material, such as adielectric oxide layer, may be formed as a thin tunneling barrier layersandwiched between the ferromagnetic layers. The layers are typicallydeposited sequentially as overlying blanketed films. The ferromagneticlayers and the insulator material are subsequently patterned by variousetching processes in which one or more layers are removed, eitherpartially or totally, in order to form a device feature.

When the respective magnetizations of the reference layer and thestorage layer are antiparallel, a resistance of the magnetic tunneljunction is high having a resistance value R_(max) corresponding to ahigh logic state “1”. On the other hand, when the respectivemagnetizations are parallel, the resistance of the magnetic tunneljunction is low, namely having a resistance value R_(min) correspondingto a low logic state “0”. A logic state of a MRAM cell is read bycomparing its resistance value to a reference resistance value R_(ref),which is derived from a reference cell or a group of reference cells andrepresents an in-between resistance value between that of the high logicstate “1” and the low logic state “0”.

Spin-transfer-torque magnetic random access memory (STT MRAM) andspin-orbit-torque magnetic random access memory (SOT MRAM) are differentchip architectures that each has its own electrical performance andenergy efficiency. A demand for hybrid and integrated spin-orbit-torquemagnetic spin-transfer-torque magnetic random access memory (SOT-STTMRAM) has recently increased due to its combined benefits. However, howto fabricate SOT-STT MRAMs with desired production yield and wellintegrated film scheme for the magnetic tunnel junction (MTJ) structureremain a challenge.

Therefore, there is a need in the art for improved methods and apparatusfor fabricating MTJ structures for MRAM applications.

SUMMARY

Embodiments of the disclosure provide methods and apparatus forfabricating magnetic tunnel junction (MTJ) structures along with a backend interconnection structure on a substrate for MRAM applications,particularly for hydride spin-orbit-torque magnetic spin-transfer-torquemagnetic random access memory (SOT-STT MRAM) applications. In oneembodiment, an interconnection structure includes a magnetic tunneljunction structures disposed on a substrate. The magnetic tunneljunction structure comprises a first ferromagnetic layer and a secondferromagnetic layer sandwiching a tunneling barrier layer, a spin orbittorque (SOT) layer disposed on the magnetic tunnel junction structureand a back end structure disposed on the spin orbit torque (SOT) layer.

In another embodiment, a method of forming an interconnection structureincludes forming a film stack having a first ferromagnetic layer and asecond ferromagnetic layer sandwiching a tunneling barrier layer on asubstrate, forming a patterned hardmask layer on the film stack,patterning the film stack using the patterning hardmask layer as anetching mask layer, forming a first insulation material to cover thepatterned hardmask layer and the film stack on the substrate, polishingthe first insulation material until a top surface of the hardmask layeris exposed, forming a spin orbit torque (SOT) layer on the top surfaceof the hardmask layer, and forming an back end interconnection structureon the spin orbit torque (SOT) layer.

In yet another embodiment, an interconnection structure for a memorydevice includes multiple magnetic tunnel junction structures connectedto a SOT layer, wherein the magnetic tunnel junction structures have acapping layer connecting the SOT layer fabricated from a material thesame from the SOT layer, and a dual damascene back end structureconnected to the SOT layer.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings.

FIG. 1 depicts one embodiment of a cluster processing system forpractice one embodiment of the present disclosure;

FIG. 2 depicts another embodiment of a cluster processing system forpractice one embodiment of the present disclosure;

FIG. 3 depicts a flow diagram illustrating a method for fabricatingmagnetic tunnel junction (MTJ) structures along with a back endinterconnection structure according to one embodiment of the presentdisclosure;

FIGS. 4A-4K are cross sectional views of a substrate at various stagesof the method of FIG. 3 ;

FIG. 5 is a cross sectional view of another example of a magnetic tunneljunction (MTJ) structure with a back end interconnection structureformed on a substrate; and

FIG. 6 is a cross sectional view of yet another example of a magnetictunnel junction (MTJ) structure with a back end interconnectionstructure formed on a substrate; and

FIG. 7 is a cross sectional view of one example of a magnetic tunneljunction (MTJ) structure that is used in FIGS. 4A-4I, FIG. 5 or FIG. 6 .

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially utilized on other embodiments withoutspecific recitation.

It is to be noted, however, that the appended drawings illustrate onlytypical embodiments of this disclosure and are therefore not to beconsidered limiting of its scope, for the disclosure may admit to otherequally effective embodiments.

DETAILED DESCRIPTION

Embodiments of the disclosure generally provide apparatus and methodsfor forming a MTJ structure and a back end interconnection structureelectrically connected to the MTJ structure disposed on a substrate forMRAM applications. The embodiments of the disclosure may be used inspin-transfer-torque magnetic random access memory (STT MRAM),spin-orbit-torque magnetic random access memory (SOT MRAM), and/or thehybrid (or called integrated) spin-orbit-torque magneticspin-transfer-torque magnetic random access memory (SOT-STT MRAM)applications. In one embodiment, while pattering the film stack forforming the MTJ structure, a hardmask may be utilized. Such hardmasklayer may be the same material of a spin orbit torque (SOT) layerdisposed on the MTJ structure. In some examples, the hardmask layer mayalso be served as the spin orbit torque (SOT) layer when the MTJstructure is patterned and formed. After the MTJ structure and the SOTlayer is formed thereon, a back end (e.g., single damascene or dualdamascene) interconnection structure may be formed on the SOT layer sothat the back end interconnection structure is in electricalcommunication to the MTJ structure. A chemical mechanical polishingprocess (CMP) may be utilized while forming the MTJ structure as well asthe back end interconnection structure. The MTJ structure as well as theback end interconnection structure may be integratedly formed in acluster processing system without transferring the substrate out of thesystem and without breaking vacuum. In some examples, multiple MTJstructures may be connected to the SOT layer that is in furtherelectrical connection to the back end (e.g., single damascene or dualdamascene) interconnection structure.

FIG. 1 is a schematic, top plan view of an exemplary cluster processingsystem 100 that includes one or more of the processing chambers 111,121, 132, 128, 120 that are incorporated and integrated therein. In oneembodiment, the cluster processing system 100 may be a Centura® orEndura® integrated processing system, commercially available fromApplied Materials, Inc., located in Santa Clara, Calif. It iscontemplated that other processing systems (including those from othermanufacturers) may be adapted to benefit from the disclosure.

The cluster processing system 100 includes a vacuum-tight processingplatform 104, a factory interface 102, and a system controller 144. Theplatform 104 includes a plurality of processing chambers 111, 121, 132,128, 120 and at least one load-lock chamber 122 that is coupled to avacuum substrate transfer chamber 136. Two load lock chambers 122 areshown in FIG. 1 . The factory interface 102 is coupled to the transferchamber 136 by the load lock chambers 122.

In one embodiment, the factory interface 102 comprises at least onedocking station 108 and at least one factory interface robot 114 tofacilitate transfer of substrates. The docking station 108 is configuredto accept one or more front opening unified pod (FOUP). Two FOUPS 106A-Bare shown in the embodiment of FIG. 1 . The factory interface robot 114having a blade 116 disposed on one end of the robot 114 is configured totransfer the substrate from the factory interface 102 to the processingplatform 104 for processing through the load lock chambers 122.Optionally, one or more metrology stations 118 may be connected to aterminal 126 of the factory interface 102 to facilitate measurement ofthe substrate from the FOUPS 106A-B.

Each of the load lock chambers 122 have a first port coupled to thefactory interface 102 and a second port coupled to the transfer chamber136. The load lock chambers 122 are coupled to a pressure control system(not shown) which pumps down and vents the load lock chambers 122 tofacilitate passing the substrate between the vacuum environment of thetransfer chamber 136 and the substantially ambient (e.g., atmospheric)environment of the factory interface 102.

The transfer chamber 136 has a vacuum robot 130 disposed therein. Thevacuum robot 130 has a blade 134 capable of transferring substrates 124among the load lock chambers 122, the metrology system 110 and theprocessing chambers 111, 121, 132, 128, 120.

In one embodiment of the cluster processing system 100, the clusterprocessing system 100 may include one or more processing chambers 111,121, 132, 128, 120, which may be a deposition chamber (e.g., physicalvapor deposition chamber, chemical vapor deposition, or other depositionchambers), annealing chamber (e.g., high pressure annealing chamber, RTPchamber, laser anneal chamber), etch chamber, cleaning chamber, curingchamber, lithographic exposure chamber, or other similar type ofsemiconductor processing chambers. In some embodiments of the clusterprocessing system 200, one or more of processing chambers 111, 121, 132,128, 120, the transfer chamber 136, the factory interface 102 and/or atleast one of the load lock chambers 122.

The system controller 144 is coupled to the cluster processing system100. The system controller 144, which may include the computing device101 or be included within the computing device 101, controls theoperation of the cluster processing system 100 using a direct control ofthe process chambers 111, 121, 132, 128, 120 of the cluster processingsystem 100. Alternatively, the system controller 144 may control thecomputers (or controllers) associated with the process chambers 111,121, 132, 128, 120 and the cluster processing system 100. In operation,the system controller 144 also enables data collection and feedback fromthe respective chambers to optimize performance of the clusterprocessing system 100.

The system controller 144, much like the computing device 101 describedabove, generally includes a central processing unit (CPU) 138, a memory140, and support circuit 142. The CPU 138 may be one of any form of ageneral purpose computer processor that can be used in an industrialsetting. The support circuits 142 are conventionally coupled to the CPU138 and may comprise cache, clock circuits, input/output subsystems,power supplies, and the like. The software routines transform the CPU138 into a specific purpose computer (controller) 144. The softwareroutines may also be stored and/or executed by a second controller (notshown) that is located remotely from the cluster processing system 100.

FIG. 2 depicts a plan view of another example of a cluster processingsystem 200 that the methods described herein may be practiced. Oneprocessing system that may be adapted to benefit from the disclosure isa 300 mm or 450 mm PRODUCER® processing system, commercially availablefrom Applied Materials, Inc., of Santa Clara, Calif. The clusterprocessing system 200 generally includes a front platform 202 wheresubstrate cassettes 218 included in FOUPs 214 are supported andsubstrates are loaded into and unloaded from a loadlock chamber 209, atransfer chamber 211 housing a substrate handler 213 and a series oftandem processing chambers 206 mounted on the transfer chamber 211.

Each of the tandem processing chambers 206 includes two process regionsfor processing the substrates. The two process regions share a commonsupply of gases, common pressure control, and common process gasexhaust/pumping system. Modular design of the system enables rapidconversion from one configuration to any other. The arrangement andcombination of chambers may be altered for purposes of performingspecific process steps. Any of the tandem processing chambers 206 caninclude a lid according to aspects of the disclosure as described belowthat includes one or more chamber configurations. It is noted that thecluster processing system 200 may be configured to perform a depositionprocess, etching process, curing processes, lithographic exposureprocess or heating/annealing process as needed.

In one implementation, the cluster processing system 200 can be adaptedwith one or more of the tandem processing chambers having supportingchamber hardware known to accommodate various other known processes suchas chemical vapor deposition (CVD), physical vapor deposition (PVD),atomic layer deposition (ALD), spin coating, etching, curing,lithographic exposure or heating/annealing process and the like. Forexample, the cluster processing system 200 can be configured with one ofthe processing chambers 206 as a chemical vapor deposition processingchamber or a physical vapor deposition chamber for forming a passivationlayer or a metal containing dielectric layers, metal layers orinsulating materials formed on the substrates. Such a configuration canenhance research and development fabrication utilization and, ifdesired, substantially eliminate exposure of films as etched toatmosphere.

A controller 240, including a central processing unit (CPU) 244, amemory 242, and support circuits 246, is coupled to the variouscomponents of the cluster processing system 200 to facilitate control ofthe processes of the present disclosure. The memory 242 can be anycomputer-readable medium, such as random access memory (RAM), read onlymemory (ROM), floppy disk, hard disk, or any other form of digitalstorage, local or remote to the cluster processing system 200 or CPU244. The support circuits 246 are coupled to the CPU 244 for supportingthe CPU in a conventional manner. These circuits include cache, powersupplies, clock circuits, input/output circuitry and subsystems, and thelike. A software routine or a series of program instructions stored inthe memory 242, when executed by the CPU 244, executes the tandemprocessing chambers 206.

FIG. 3 depicts a flow diagram illustrating a process 300 formanufacturing MTJ structures and back end interconnection structures ona substrate for MRAM applications according to one embodiment of thepresent disclosure. It is noted that the process 300 for manufacturingMTJ structures and back end interconnection structures may be utilizedin spin-transfer-torque magnetic random access memory (STT MRAM),spin-orbit-torque magnetic random access memory (SOT MRAM), and/or thehybrid (or called integrated) spin-orbit-torque magneticspin-transfer-torque magnetic random access memory (SOT-STT MRAM)applications, particularly in hybrid (or called integrated)spin-orbit-torque magnetic spin-transfer-torque magnetic random accessmemory (SOT-STT MRAM) applications. FIGS. 4A-4K are schematiccross-sectional views of an interconnection structure 450 formed on asubstrate 402 at various stages of the process of FIG. 3 . It iscontemplated that the process 300 may be performed in suitableprocessing chambers, including deposition chambers, etching chambers orother suitable processing chambers incorporated in the clusterprocessing systems 100 or 200 depicted in FIGS. 1 and 2 . It is alsonoted that the process 300 may be performed in suitable processingchambers, including those from other manufacturers.

The process 300 begins at operation 302 by providing a substrate, suchas the substrate 402 having a first interconnection structure 407 formedin a first insulating structure 404, as shown in FIG. 4A. The firstinterconnection structure 407 and the first insulating structure 404 maybe formed in one or more of the processing chambers incorporated in thecluster processing system 100 or 200 depicted in FIGS. 1 and 2 . In oneembodiment, the substrate 402 comprises metal or glass, silicon,dielectric bulk material and metal alloys or composite glass,crystalline silicon (e.g., Si<100> or Si<111>), silicon oxide, strainedsilicon, silicon germanium, germanium, doped or undoped polysilicon,doped or undoped silicon wafers and patterned or non-patterned waferssilicon on insulator (SOI), carbon doped silicon oxides, siliconnitride, doped silicon, germanium, gallium arsenide, glass, or sapphire.The substrate 402 may have various dimensions, such as 200 mm, 300 mm,450 mm or other diameter, as well as, being a rectangular or squarepanel. Unless otherwise noted, examples described herein are conductedon substrates with a 200 mm diameter, a 300 mm diameter, or a 450 mmdiameter substrate. In one embodiment, the substrate 402, as shown inFIG. 4A, includes the first interconnection structure 407 formed in thefirst insulating structure 404 disposed on the substrate 402.

The first insulating structure 404 may comprise a dielectric material,such as SiN, SiCN, SiO₂, SiON, SiC, amorphous carbon, SiOC or othersuitable low dielectric constant material and the like. The firstinterconnection structure 407 includes a metal containing material, suchas aluminum, tungsten, copper, nickel, and the like. In one example, thefirst insulating structure 404 includes a low dielectric constantdielectric material, such as SiOC, and the first interconnectionstructure 407 includes copper.

At operation 304, a film stack 406 and a hardmask layer 414 are disposedon the substrate 402, as shown in FIG. 4B. The film stack 406 and thehardmask layer 414 may be formed in one or more of the processingchambers incorporated in the cluster processing system 100 or 200depicted in FIGS. 1 and 2 . The film stack 406 further includes a firstferromagnetic layer 412 and a second ferromagnetic layer 408 sandwichinga tunneling barrier layer 410. Though the film stack 406 described inFIGS. 4B-4K only includes three layers, it is noted that additional ormultiple film layers can be further formed in the film stack 406 asneeded. One of the examples of the additional or multiple film layersformed in the film stack 406 is further described below with referenceto FIG. 7 . The tunneling barrier layer 410 may be an oxide barrierlayer in the case of a tunnel junction magnetoresistive (TMR) sensor ora conductive layer in the case of a giant magnetoresistive (GMR) sensor.When the film stack 406 is configured to form a TMR sensor, then thetunneling barrier layer 410 may comprise MgO, HfO₂, TiO₂, TaO_(x),Al₂O₃, or other suitable materials. In the embodiment depicted in FIGS.4B-4K, the tunneling barrier layer 410 may comprise MgO having athickness of about 1 to about 15 Angstroms, such about 10 Angstroms.

The first and second ferromagnetic layers 412, 408 may be a metalcontaining material or a magnetic material, such as Mo, Ir, Ru, Ta, MgO,Hf, CoFe, CoFeB and the like. It is noted that the first and secondferromagnetic layers 412, 408 may be fabricated from the same ordifferent materials as needed.

The hardmask layer 414 is disposed on the film stack 406 and will belater utilized as an etching mask layer during the following patterningand/or etching process. The hardmask layer 414 is formed from a materialthat is similar to or the same as a spin-orbit-torque (SOT) layer 424(shown in FIG. 4I), which will be later formed thereon. In one example,the hardmask layer 414 is fabricated from CoFeB, MgO, Ta, W, Pt, CuBi,Mo, Ru, alloys thereof, or combinations thereof.

At operation 304, a patterning process, e.g., an etching process, isfirst performed to pattern the hardmask layer 414, forming an openingarea 416 in the hardmask layer 414, as shown in FIG. 4C. The firstpatterning process may be performed in one or more of the processingchambers incorporated in the cluster processing system 100 or 200depicted in FIGS. 1 and 2 . The opening area 416 formed in the hardmasklayer 414 expose a portion of the film stack 406 for patterning so as toform a magnetic tunnel junction (MTJ) structure 452 (shown in FIG. 4D)with a desired dimension from the film stack 406.

At operation 308, a second patterning process is performed to pattern(e.g., etch) the film stack 406 exposed by the patterned hardmask layer414 to form a magnetic tunnel junction (MTJ) structure 452, as shown inFIG. 4D, until the underlying first insulating material 404 is exposed.The second patterning process may be performed in one or more of theprocessing chambers incorporated in the cluster processing system 100 or200 depicted in FIGS. 1 and 2 . It is noted that the patterned hardmasklayer 414 is intended to be left and remained on the film stack 406,forming as part of the magnetic tunnel junction (MTJ) structure 452after the patterning process performed at operation 308. Thus, noadditional ash or stripping process is required to remove the hardmasklayer 414 after the second patterning process. The second patterningprocess for patterning the film stack 406 may include several steps ordifferent recipes configured to supply different gas mixtures oretchants to etch different layers in accordance with the materialsincluded in each layer.

During patterning, an etching gas mixture or several gas mixtures withdifferent etching species are sequentially supplied into the substratesurface to remove the portion of the film stack 406 exposed by thepatterned hardmask layer 414 from the substrate 402.

The end point of the patterning process at operation 308 may becontrolled by time or other suitable method. For example, the patterningprocess may be terminated after performing for between about 200 secondsand about 10 minutes until the underlying first insulating material 404is exposed, as shown in FIG. 4D. The patterning process may beterminated by determination from an endpoint detector, such as an OESdetector or other suitable detector as needed.

It is noted that although the profile of the magnetic tunnel junction(MTJ) structure 452 as formed after patterning the film stack 406 has atapered sidewalls, it is noted that the magnetic tunnel junction (MTJ)structure 452 may have substantially vertical sidewall profiles or anysuitable sidewall profiles with desired slopes as needed.

At operation 310, after the patterning process, a deposition process isperformed to form a second insulating structure 418 on the magnetictunnel junction (MTJ) structure 452 (e.g., including the patternedhardmask layer 414 and the patterned film stack 406), as shown in FIG.4E. The second insulating structure 418 may be formed in one or more ofthe processing chambers incorporated in the cluster processing system100 or 200 depicted in FIGS. 1 and 2 . The second insulating structure418 is formed having a sufficient thickness to cover the magnetic tunneljunction (MTJ) structure 452. The second insulating structure 418 may bea dielectric layer formed by a deposition process performed after thepatterning process at operation 308. The second insulating structure 418may be the same or similar to the first insulating structure 404. In oneexample, the second insulating structure 418 includes a low dielectricconstant material comprising SiOC.

At operation 312, a chemical mechanical polishing process is performedto polish away the excess second insulating structure 418 so as toexpose a top surface 435 of the magnetic tunnel junction (MTJ) structure452 (e.g., a top surface 435 of the patterned hardmask layer 414), asshown in FIG. 4F, so that the top surface 435 of the patterned hardmasklayer 414 is substantially coplanar with the second insulating structure418. The CMP process as performed may remove the excess secondinsulating structure 418 without adversely damaging or over-polishingthe nearby materials when the magnetic tunnel junction (MTJ) structure452 is exposed. By using a relatively low polishing downforce and slowpolishing rate, the second insulating structure 418 may be removedwithout damaging or over polishing away material from the magnetictunnel junction (MTJ) structure 452.

The chemical mechanical polishing process may remove or polish thesecond insulating structure 418 by using a fluid supplied during thepolishing process, or by DI water. A relatively soft polishing pad, suchas a pad having elasticity greater 90% may be used to during thechemical mechanical polishing process. During polishing, as thepolishing pad selected has a relatively soft surface, thus, slurry orother chemical fluid may be eliminated as needed. In one example, DIwater may be utilized during the chemical mechanical polishing process.The chemical mechanical polishing process is followed by a cleaningprocess as needed to enhance the cleanliness of the substrate surface.

At operation 314, a third insulating structure 420 is formed on themagnetic tunnel junction (MTJ) structure 452 and the second insulatingstructure 418, as shown in FIG. 4G. The third insulating structure 420may be formed in one or more of the processing chambers incorporated inthe cluster processing system 100 or 200 depicted in FIGS. 1 and 2 .Similarly, the third insulating structure 420 may be formed from anysuitable deposition techniques, such as CVD, ALD, PVD, spin-coating,spray coating or any suitable deposition processes. The third insulatingstructure 420 may be the same or similar to the first or secondinsulating structure 404, 418. In one example, the third insulatingstructure 420 includes a low dielectric constant material comprisingSiOC.

At operation 316, another patterning process is performed to form anopening 422 in the third insulating structure 420 to expose the topsurface 435 of the magnetic tunnel junction (MTJ) structure 452, asshown in FIG. 4H. The pattering process may be performed in one or moreof the processing chambers incorporated in the cluster processing system100 or 200 depicted in FIGS. 1 and 2 . One or more patterning masks (notshown) may be utilized to assist forming the opening 422 in the thirdinsulating structure 420. The patterning process is performed to patternthe third insulating structure 420 until the top surface 435 of themagnetic tunnel junction (MTJ) structure 452 is exposed.

At operation 318, a deposition process is performed to form a spin orbittorque (SOT) layer 424 on the substrate, filling the opening 422 definedin and above the third insulating structure 420, as shown in FIG. 4I.The deposition process may be performed in one or more of the processingchambers incorporated in the cluster processing system 100 or 200depicted in FIGS. 1 and 2 . The material of the spin orbit torque (SOT)layer 424 is selected to be similar or the same as the hardmask layer414 so as to promote the electrical performance of the magnetic tunneljunction (MTJ) structure 452. Furthermore, as the material of the spinorbit torque (SOT) layer 424 and the hardmask layer 414 are similar orthe same, the manufacturing concerns or complexity may be reduced as theadhesion control at the interface between the spin orbit torque (SOT)layer 424 and the hardmask layer 414 is relatively easy and compatible.The hardmask layer 414 remained in the magnetic tunnel junction (MTJ)structure 452 may also serve as a capping layer to provide a goodelectrical contact to the spin orbit torque (SOT) layer 424. In oneembodiment, the spin orbit torque (SOT) layer 424 is fabricated from Ta,Ru, MgO, W, Pt, CuBi, Mo, or combinations thereof.

At operation 320, a chemical mechanical polishing process is furtherperformed to polish away the excess spin orbit torque (SOT) layer 424 soas to have a top surface 425 of the spin orbit torque (SOT) layer 424substantially coplanar with a top surface 426 of the third insulatingstructure 420, as shown in FIG. 4J. The CMP process as performed mayremove the excess spin orbit torque (SOT) layer 424 without adverselydamaging or over-polishing the nearby materials so that the excess spinorbit torque (SOT) layer 424 can be filled in the third insulatingstructure 420 with the desired dimension to provide electricalconnection to the underlying magnetic tunnel junction (MTJ) structure452. By using a relatively low polishing downforce and slow polishingrate, the excess spin orbit torque (SOT) layer 424 may be removed,without damaging or over polishing away material from the magnetictunnel junction (MTJ) structure 452 and the third insulating structure420.

After the SOT layer 424 is formed in the third insulating structure 420,an additional interconnection structure 432 is formed above the spinorbit torque (SOT) layer 424 to provide electrical connection and/orcommunication to the magnetic tunnel junction (MTJ) structure 452, asshown in FIG. 4K. The additional interconnection structure 432 is alsoformed in a fourth insulating structure 430 to form a back end structurethat has electrical contact and communication to the magnetic tunneljunction (MTJ) structure 452. The additional interconnection structure432 formed in the fourth insulating structure 430 is a single damascenestructure. It is noted that the additional interconnection structuresmay be formed in other forms, such as dual damascene structure or othersuitable structures.

FIG. 5 depicts another example of an interconnection structure 550formed on the substrate 402. Similar to the interconnection structure450 depicted in FIG. 4K, the interconnection structure 550 includes thefirst interconnection structure 407 formed in the first insulatingstructure 404, the magnetic tunnel junction (MTJ) structure 452 formedon the first interconnection structure 407 and a SOT layer 424 formed onthe magnetic tunnel junction (MTJ) structure 452. However, the SOT layer424 in this example as shown in FIG. 5 has a relatively longer widththat allows additional two upper interconnection structures 504 a, 504 bformed thereon. The two upper interconnection structures 504 a, 504 beach has a first conductive line 506 a, 506 b connecting to the SOTlayer 424 while a second conductive line 508 a, 508 b connecting to twolower interconnection structures 502 a, 502 b. The upper interconnectionstructures 504 a, 504 b as utilized here are dual damascene structures.The two upper interconnection structures 504 a, 504 b are in directcontact and in electrical connection/communication with the two lowerinterconnection structures 502 a, 502 b through the second conductiveline 508 a, 508 b. The first interconnection structure 407 and themagnetic tunnel junction (MTJ) structure 452 may be verticallyinterposed between the two upper interconnection structures 504 a, 504 band the two lower interconnection structures 502 a, 502 b, as shown inFIG. 5 .

FIG. 6 depicts yet another example of an interconnection structure 650formed on the substrate 402. The interconnection structure 650 comprisesmultiple, such as three, magnetic tunnel junction (MTJ) structures 452a, 452 b, 452 c each formed on a lower interconnection structure 602 a,602 b, 602 c. The SOT layer 424 has a relatively long width so as toallow additional two upper interconnection structures 640 a, 640 bformed on the SOT layer 424. In this example, the upper interconnectionstructures 640 a, 640 b are not in direct contact with the lowerinterconnection structures 602 a, 602 b, 602 c. Instead, the upperinterconnection structures 640 a, 640 b is in electricalconnection/communication with the lower interconnection structures 602a, 602 b, 602 c through the SOT layer 424 and the three magnetic tunneljunction (MTJ) structures 452 a, 452 b, 452 c interposed therebetween.By utilizing the multiple magnetic tunnel junction (MTJ) structures 452a, 452 b, 452 c and the interconnection structures 602 a, 602 b, 602 c,640 a, 640 b, the electrical performance may be enhanced and devicedensities may be increased.

FIG. 7 depicts another example of a magnetic tunnel junction (MTJ) 702.The magnetic tunnel junction (MTJ) 702 may be utilized as the magnetictunnel junction (MTJ) 452 depicted in FIGS. 4K, 5 and 6 as well. Themagnetic tunnel junction (MTJ) 702 includes the film stack 406 depictedabove with the first ferromagnetic layer 412 and the secondferromagnetic layer 408 sandwiching the tunneling barrier layer 410. Inadditional to the film stack 406, a seed layer 710 may be formed in abottom of the magnetic tunnel junction (MTJ) 702. The materials may beutilized to form the seed layer 710 including NiCr, Pt, Cr, CoFeB, Ta,Ru, TaN, alloys or combinations thereof. A pinned layer 708 may beformed on the seed layer 710. The pinned layer 708 may comprise one ormore of several types of pinned layers, such as a simple pinned,antiparallel pinned, self-pinned or antiferromagnetic pinned sensor. Inone example depicted in FIG. 7 , the pinned layer 708 includes multiplelayers, such as four layers. It is noted that the number of the pinnedlayer 708 may be any number as needed. The pinned layer 708 may beconstructed of several magnetic materials such as a metal alloy withdopants, such as boron dopants, oxygen dopants or other suitablematerials. Metal alloys may be a nickel containing material, platinumcontaining material, Ru containing material, a cobalt containingmaterial, tantalum containing materials and palladium containingmaterials. Suitable examples of the magnetic materials that may comprisethe pinned layer 708 include Ru, Ta, Co, Pt, Ni, TaN, NiFeO_(x), NiFeB,CoFeO_(x)B, CoFeB, CoFe, NiO_(x)B, CoBO_(x), FeBO_(x), CoFeNiB, CoPt,CoPd, TaO_(x) and the like.

An Ruderman-Kittel-Kasuya-Yosida (RKKY) layer 706 (also called acoupling layer) may be disposed on the pinned layer 708 below the filmstack 406. The RKKY layer 706 may be formed to control spin directionsin the magnetic tunnel junction (MTJ) 702. The materials utilized tofabricate the RKKY layer 706 include Ir, Ru, Ta, W, Mo, alloys thereof,or combinations thereof.

A capping layer 704 may be formed on the film stack 406. In the exampledepicted above, the capping layer 704 may be the patterned hardmasklayer 414 described above with reference to FIGS. 4I, 5 and 6 . In someexamples, additional capping layers may be formed on the film stack 406,on the patterned hardmask layer 414 or other suitable positions in themagnetic tunnel junction (MTJ) 702 as needed. Suitable examples of thecapping layer 704 (or the patterned hardmask layer 414) include one ormore layers of at one or more of CoFeB, MgO, Ta, W, Pt, CuBi, Mo, Ru,alloys thereof and combinations thereof. In one example, the film stack710 in total includes multiple layers including TaN, NiCr, Co, Ni, Ir,Co or Ni, Mo, CoFeB, MgO, CoFeB, Mo, CoFeB, MgO, CoFeB, Mo and Rulayers.

In the example depicted in FIG. 7 , all these layers or film stack 710,708, 706, 406, 704 may be formed by any suitable techniques, such asCVD, PVD, ALD, spin-coating, spray coating, and any suitable manners.One example of systems that may be used to form these layers includesCENTURA®, PRECISION 5000® and PRODUCER® deposition systems, allavailable from Applied Materials Inc., Santa Clara, Calif., or fromother manufactures. It is contemplated that other processing system,including those available from other manufacturers, may be adapted topractice the disclosure. It is noted that all these layers and filmstack 710, 708, 706, 406, 704 in the magnetic tunnel junction (MTJ) 702may be formed in one or more processing chambers incorporated in thecluster processing system 100, 200 depicted in FIGS. 1 and 2 .

Accordingly, processes and apparatus of forming MTJ device structuresfor MRAM are provided, particularly for hybrid (or called integrated)spin-orbit-torque magnetic spin-transfer-torque magnetic random accessmemory (SOT-STT MRAM) applications. In one embodiment, while pattering afilm stack for forming the MTJ structure, a hardmask may be utilized.Such hardmask layer may be the same material of a spin orbit torque(SOT) layer disposed on the MTJ structure. In some examples, thehardmask layer may also be served as the spin orbit torque (SOT) layerwhen the MTJ structure is patterned and formed. After the MTJ structureand the SOT layer is formed thereon, a back end (e.g., single damasceneor dual damascene) interconnection structure may be formed on the SOTlayer so that the back end interconnection structure is in electricalcommunication to the MTJ structure. Multiple back end structures and MTJstructures may be utilized to enhance the densities and electricalperformance of the MRAM devices.

While the foregoing is directed to embodiments of the disclosure, otherand further embodiments of the disclosure may be devised withoutdeparting from the basic scope thereof.

What is claimed is:
 1. A method of forming an interconnection structurecomprising: forming a film stack having a first ferromagnetic layer anda second ferromagnetic layer sandwiching a tunneling barrier layer on asubstrate; forming a patterned hardmask layer on the film stack;patterning the film stack using the patterned hardmask layer as anetching mask layer; forming a first insulation material to cover thepatterned hardmask layer and the film stack on the substrate; polishingthe first insulation material until a top surface of the patternedhardmask layer is exposed; forming a spin orbit torque (SOT) layer onthe top surface of the patterned hardmask layer; and forming a firstback end interconnection structure on the SOT layer.
 2. The method ofclaim 1, wherein the film stack and the patterned hardmask layer incombination form a magnetic tunnel junction structure.
 3. The method ofclaim 1, wherein the SOT layer is fabricated from the same material fromthe patterned hardmask layer.
 4. The method of claim 1, wherein the SOTlayer and the patterned hardmask layer are fabricated from a materialselected from a group consisting of CoFeB, MgO, Ta, W, Pt, CuBi, Mo andRu.
 5. The method of claim 1, wherein the first back end interconnectionstructure is a dual damascene structure.
 6. The method of claim 1,wherein forming the SOT layer comprises: forming a patterned insulatinglayer having an opening exposing the patterned hardmask layer; andforming the SOT layer in the opening.
 7. The method of claim 6 furthercomprising: polishing the SOT layer and the patterned insulating layerso that a top surface of the SOT layer is substantially coplanar withthe patterned insulating layer.
 8. The method of claim 1, wherein alower interconnection structure is connected to the film stack.
 9. Themethod of claim 8, wherein the first back end interconnection structureis connected to the lower interconnection structure.
 10. The method ofclaim 1 further comprising forming a second back end interconnectionstructure on the SOT layer.
 11. A processing system comprising: one ormore processing chambers configured to: form a film stack having a firstferromagnetic layer and a second ferromagnetic layer sandwiching atunneling barrier layer on a substrate; form a patterned hardmask layeron the film stack; pattern the film stack using the patterned hardmasklayer as an etching mask layer; form a first insulation material tocover the patterned hardmask layer and the film stack on the substrate;polish the first insulation material until a top surface of thepatterned hardmask layer is exposed; form a spin orbit torque (SOT)layer on the top surface of the patterned hardmask layer; and form afirst back end interconnection structure on the SOT layer.
 12. Theprocessing system of claim 11, wherein the film stack and the patternedhardmask layer in combination form a magnetic tunnel junction structure.13. The processing system of claim 11, wherein the SOT layer isfabricated from the same material from the patterned hardmask layer. 14.The processing system of claim 11, wherein the SOT layer and thepatterned hardmask layer are fabricated from a material selected from agroup consisting of CoFeB, MgO, Ta, W, Pt, CuBi, Mo and Ru.
 15. Theprocessing system of claim 11, wherein the first back endinterconnection structure is a dual damascene structure.
 16. Theprocessing system of claim 11, wherein forming the SOT layer comprises:forming a patterned insulating layer having an opening exposing thepatterned hardmask layer; and forming the SOT layer in the opening. 17.The processing system of claim 16, wherein the one or more processingchambers are further configured to: polish the SOT layer and thepatterned insulating layer so that a top surface of the SOT layer issubstantially coplanar with the patterned insulating layer.
 18. Theprocessing system of claim 11, wherein a lower interconnection structureis connected to the film stack.
 19. The processing system of claim 18,wherein the first back end interconnection structure is connected to thelower interconnection structure.
 20. The processing system of claim 11,wherein the one or more processing chambers is further configured toform a second back end interconnection structure on the SOT layer.